Abstract
Based on the basic theory of vacuum preloading, this paper proposes an good effect of pressurized vacuum preloading in which the high pressure gas results in tiny cracks between the air pressurized pipe and band drain. Therefore additional drainage paths are introduced to improve the permeability of soil and accelerate soil consolidation. But field tests show that the advantages of pressurized vacuum preloading are not obvious compared with conventional vacuum preloading, and the soil settlement, soil properties and vane shear strength are slightly lower than those by conventional vacuum preloading. The vacuum pressure transmission is analysed in the air pressurized pipe and band drain as well as the dissipation of pore water pressure in the soil during the pressurization process, it is concluded that the unsatisfactory reinforcement effect is mainly due to the sealing problem between the top of the air pressurized pipe and the sand cushion, and the overlap problem between the booster pipe and band drain.
Highlights
In recent years, there were some problems that have plagued engineers during vacuum preloading and reinforcement for soft soil ground
The reinforcement mechanism of the pressurized vacuum preloading should be: in the process of vacuum preloading, by introducing high pressure gas, lots of tiny cracks are generated between the booster pipe and the band drain to form additional drainage channels and improve the permeability of soil
The main differences between pressurized vacuum preloading and ordinary vacuum preloading are: 1After the plastic band drain is installed, the booster pipeline is arranged; 2When the duration of vacuum pre-pressure reaches 103 d, air pressurization starts and continue for 18 d, and the boost pressure is kept between 600 kPa and 800 kPa. the vacuum is continued until unloading
Summary
There were some problems that have plagued engineers during vacuum preloading and reinforcement for soft soil ground. In order to solve the above problems, Jin et al [2] proposed a pressurized vacuum preloading method This method is setting a pressure boosting pipe in the soil to increase the pressure difference between the band drain and the surrounding soil, which is improving the reinforcement effect of the vacuum preloading. Lei et al [4] carried out microstructural testing of the ultra-soft soil under dredging by means of electron microscopy (SEM) and mercury intrusion test (MIP) It is proved from the microscopic point that the pressurized vacuum preloading effect is better than the ordinary vacuum preheating. In terms of engineering application, Lin et al [6] combined with the Zhuhai West Station foundation treatment project, proved that the Pressurized vacuum preloading can greatly increase the settlement during the reinforcement period and achieve better soft foundation treatment. The laboratory contrast test has proved that the pressurized vacuum preloading is better than the ordinary vacuum preloading, application of project examples is necessary to evaluate the reinforcement effect of pressurized vacuum preloading
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